As mobile services have evolved in recent years, a variety of service models utilizing smart phones have been developing. Among these, some service uses proximity of users. Use of a cellular network to provide such a service may cause data congestion as the number of users increases. To solve the problems caused by the data congestion, the device-to-device communication (D2D) technology using proximity of communication terminals has been proposed.
The D2D communication may be performed between terminals to use radio resources effectively, and a whole network throughput may increase due to direct path communication performed by the D2D communication. However, when a distance between communication terminals is relatively great, the D2D communication is inefficient due to deterioration in the quality of radio channels and thus communicating via a default path of the cellular network is more efficient. Therefore, it is preferable that the direct path switches to the default path according to the quality of radio channels between terminals. In addition, since the cellular network should guarantee mobility of terminals, it may be necessary to switch between the default path and the direct path when the terminal moves.
Therefore, there is a need for an effective method for switching between a default path and a direct path by considering a state of a terminal.